textproduct: Albany

SYNOPSIS

After a mild but mostly cloudy afternoon, a cold frontal passage this evening into tonight will bring scattered showers and a return to below normal temperatures. In the wake of the cold front, lake effect snow is expected to impact the southern Adirondacks, Mohawk Valley, and possibly the northern Catskills with up to several inches of snow possible. We remain in an active pattern beyond that, with additional rain/snow chances Sunday and again towards the middle of next week.

SHORT TERM /THROUGH SATURDAY/

Key Messages:

- A period of lake effect snow is expected later Thursday through Friday across portions of the Adirondacks and Mohawk Valley. Snowfall amounts of 6 to 12 inches are expected in the most persistent lake effect bands.

- A Lake Effect Snow Warning remains in effect for Northern Herkimer and Hamilton County from Thursday afternoon into Friday night. Southern Herkimer County has been added to the lake effect snow warning, and winter weather advisories for lake effect snow have been issued for Fulton, Montgomery, and Schoharie Counties from Thursday night through Saturday morning.

- Wind gusts between 30 and 40 mph on Thursday and Friday could lead to areas of blowing and drifting snow.

Discussion:

As of 7:20 PM EST...A 993 mb occluded low remains located over the Great Lakes, and is vertically stacked beneath a potent upper-level low (ULL) as seen on GOES 16 WV imagery. The system's cold front continues to track through the region this evening from west to east with a period of rain and gusty northwesterly winds gusting to 30-40mph as the rain arrives. NYS mesonet and ASOS stations show multiple sites gusting up to 30-40mph this evening as the front pushes through. Gusty winds and rain showers should diminish towards Midnight from west to eat, with temperatures falling into the 20s (terrain) to 30s (valleys) within the cold advection regime.

Thursday and Thursday night...Thursday starts off mostly dry, but with the strong southwest flow a band of snow will develop off of Lake Erie, and some fragments of this band could extend all the way into the Mohawk Valley or southeastern ADKs Thursday. Any snow showers from this Lake Erie band will generally be light with little to no accumulation in our CWA. A separate band of snow off of Lake Ontario will be oriented towards the St. Lawrence Valley through the first half of the day, but will eventually drop south at some point Thursday afternoon or evening. Exactly when this happens remains a point of forecast uncertainty. Elsewhere across the region, a few light snow showers can't be ruled out but it will be generally dry for Thanksgiving. Winds remain gusty at 20-30 mph, so with highs only in the 30s to around 40 it will feel quite chilly.

Thursday night through Friday night...This is the main period of focus for the lake effect snow across our area. As the ULL tracks north of the International border, low-level flow trajectories switch more to the west Thursday night and eventually W/NW Friday into Friday night. This will allow the band to continue to drop south Thursday night, where it will remain across northern Herkimer and northwestern Hamilton Counties. With considerable lake-induced instability (850 mb temps of -8 to -10C and Lake Ontario water temps of +8 to +10C) as well as good saturation and lift through the DGZ, snowfall rates will likely exceed 1" per hour and may reach or exceed 2" per hour across portions of northern Herkimer County. We have continued the lake effect snow warning there, and are still expecting up to 6-12" of snow where the band is most persistent. Lows Thursday night will be in the 20s region- wide.

Late Thursday night or Friday morning, the lake effect band drops southwards into the Mohawk Valley. Exactly how quickly this happens remains a big point of uncertainty, but the Thruway looks to be in the lake band possibly by 12z and certainly by 15z Friday morning. Some low-level directional shear may briefly disrupt the intensity and inland extent of the band as it is dropping south, but nevertheless moderate to heavy snowfall rates will still result in very difficult travel conditions within the band.

By Friday afternoon, low-level directional shear abates and the band should once again become more organized. With inversion heights remaining above 700 mb, 850 mb winds of around 40 kt, and a multi-lake connection developing, the band will extend well inland, likely bringing snow all the way into the high terrain of western New England where there will be some upslope enhancement. Probably the biggest forecast challenge is exactly where the band will set up. Some sources of guidance favor the band to sit almost over or just south of the Thruway, while other sources have it settling slightly further south across the sawtooth of southern Herkimer County and Schoharie Valley, extending into the Hudson Valley. Given this uncertainty, have taken a middle- ground approach for now. Will note, however, that we did increase snowfall amounts to up to a couple inches for areas just south of the immediate Capital District given the expected inland extent of the band. Wherever the band sets up, it will likely remain fairly stationary into Friday night, then may shift back slightly further north after midnight Friday night, potentially putting more of the Mohawk Valley in play. However, by this time, winds will be starting to weaken and inversion heights will be lowering, so the inland extent and intensity of the band should both be reduced.

Given all of the above, we upgraded southern Herkimer County to a Lake Effect Snow warning, as somewhere will likely see >7", with the most likely areas just south of the Thruway. We have also issued winter weather advisories for Fulton, Montgomery, and Schoharie Counties where >4" of snow is possible. Best chance for these higher snowfall amounts is in western portions of Fulton/Montgomery and northern Schoharie. Timing for the advisories and the new warning will be 06z Friday to 12z Saturday. Fulton and/or Montgomery Counties may be able to be trimmed out of the advisory earlier than 12z Saturday if the band does indeed settle a little bit further to the south. While some lake effect snow showers will likely linger into Saturday morning for the far western Mohawk Valley, snowfall rates and amounts will be much lighter than on Friday. Snow showers here should come to an end by Saturday afternoon.

The other story will be the winds Thursday night and Friday. Winds remain gusty out of the northwest, but will be stronger on Friday at 30-40 mph, especially where flow is channeled down the Mohawk Valley, through the Capital District, and into the Berkshires. While it looks very borderline whether or not winds will hit advisory criteria (46 mph), the wind will lead to blowing and drifting of snow that has already fallen, potentially making it difficult to keep roads clear. Within the lake effect bands (especially the further west one goes), the combination of moderate to heavy snow along with the wind will likely lead to significantly reduced visibilities and very difficult travel conditions. Temperatures will be mainly in the 20s (terrain) to 30s (valleys) Friday and Saturday with lows Friday night in the 20s.

LONG TERM /SATURDAY NIGHT THROUGH WEDNESDAY/

Surface high pressure and upper ridging briefly build over the region Saturday evening and night, but clouds will be on the increase ahead of our next weather system. A negatively tilted upper shortwave will be tracking from the Ohio Valley through the Great Lakes and Sunday. Ahead of this system, the isentropic lift and warm advection ahead of its warm front will lead to precipitation breaking out across the region Sunday morning. Valley areas may see some brief snow or a rain/snow mix at the onset, but then transition to plain rain as we warm through the day. Higher elevation areas may see more in the way of snow, with a couple to a few inches possible. Precipitation becomes more widespread (mainly rain for valley and rain/snow for the high terrain) with the system's cold frontal passage Sunday night.

Depending on the exact track of the system, we may see another round of lake effect snow in its wake Sunday night into Monday, but it is too early to pin down the location of any potential lake effect bands right now. Nevertheless, we have high confidence that any resulting lake effect will be much less than what is expected Thursday night and Friday.

As the system's cold front tracks off to our east, broad upper troughing remains over the eastern half to 2/3 of the CONUS. A southern stream shortwave will be tracking around the periphery of the upper trough. As it emerges off the east coast, cyclogenesis will take place. Whether the resulting sfc low tracks south and east of our region out to sea or gets close enough to bring precipitation (snow) to the region remains to be seen. If the southern stream feature is more progressive and can go negatively tilted, this would increase the chances of at least our southeastern areas getting in on the precip. However, if the southern stream feature is slower and the whole upper flow configuration remains more positively tilted then a more out to sea scenario would be likely. Sunday will be the warmest day of the long term with highs in the 30s (terrain) to 40s (valleys), with more below normal temperatures for early to the middle of next week.

AVIATION /00Z THURSDAY THROUGH MONDAY/

Through 00z Friday...A line of rain ahead of a cold front continues to track eastward this evening towards ALB, GFL and PSF which will result in a 1-3 hour period of steady rain leading to MVFR or even brief IFR vis and gusty westerly winds becoming sustained 10-15kts and gusts up to 25-30kts. We included a TEMPO group mainly from 00 to 03 UTC to highlight this potential. Once the rain exits by 02-04 UTC, much drier air behind the cold front will lead to VFR vis/cigs for the remainder of the night at all terminals. Once we reach our convective temperature tomorrow morning by 14-15 UTC, stratocu redevelop with cigs around 4-5kft but expecting VFR conditions through 00 UTC/Friday.

Westerly wind gusts up to 25-30kts expected mainly through 03-04 UTC before winds trend weaker with sustained winds around 5-8kts overnight. Winds turn gusty tomorrow morning by 14-15 UTC becoming sustained 10-12kts with gusts up to 25-30 kts.

Outlook...

Thursday Night: Low Operational Impact. Breezy. Slight Chance of SHSN. Friday: High Operational Impact. Windy With Gusts To 38 kts. Likely SHSN. Friday Night: Low Operational Impact. Breezy. Slight Chance of SHSN. Saturday: Low Operational Impact. Breezy. NO SIG WX. Saturday Night: Low Operational Impact. NO SIG WX. Sunday: High Operational Impact. Likely SHRA...SHSN. Sunday Night: Moderate Operational Impact. Chance of SHRA...SHSN. Monday: Low Operational Impact. NO SIG WX.

ALY WATCHES/WARNINGS/ADVISORIES

CT...None. NY...Lake Effect Snow Warning from 4 PM Thursday to 1 AM EST Saturday for NYZ032-033. Lake Effect Snow Warning from 1 AM Friday to 7 AM EST Saturday for NYZ038. Winter Weather Advisory from 1 AM Friday to 7 AM EST Saturday for NYZ039-040-047-082. MA...None. VT...None.